Circuit breaker having inertial delay



Feb. 24, 1970 L. N. MERRIKEN ET AL 3,497,838

CIRCUIT BREAKER HAVING INER'IIAL DELAY Filed April 22, 1968 5Sheets-Sheet 1 FIG. 5.

INVENTORS Lya/ N. Merr/ken George S. Harper ATTORNEYS Feb. 24, 1970MERR|KEN ETAL 3,497,838

CIRCUIT BREAKER HAVING INERTIAL DELAY Filed April 22, 1968 5Sheets-Sheet a FIG. 2.

INVEN'ZORS Lya/ /V. Men/ken George 8. Harper ATTORNEYS Feb. 24, 1970MERR|KEN ET AL 3,497,838

CIRCUIT BREAKER HAVING INERTIAL DELAY 5 Sheets-Sheet 3 Filed April 22.1968 FIG. 3.

INVENTORS Lya/ /V. Merrl'ken George 8 Harper ATTORNEYS FebQ24, 1970MERRlKEN ET AL 3,497,838

CIRCUIT BREAKER HAVING INERTIAL DELAY 5 Sheets-Sheet 4 Filed April 22,1968 FIG. 4.

A r V ($1 um mllllllll llllllmmn Lya/ N. Merri/ren George .5. HarperATTORNEYS Feb. 24, 1970 1.. N. MERRIKEN ET AL 3,497,838

CIRCUIT BREAKER HAVING INERTIAL DELAY 5 Sheets-Sheet 5 Filed April 22.1968 INVENTORS y Mo, r a 8H 3 N6 mm Nb ATTORNEYS United States Patent3,497,838 CIRCUIT BREAKER HAVING INERTIAL DELAY Lyal N. Merriken andGeorge S. Harper, Cambridge, Md.,

assignors to Airpax Electronics Incorporated, Cambridge, Md., acorporation of Maryland Continuation-impart of application Ser. No.545,434, Apr. 26, 1966. This application Apr. 22, 1968, Ser. No. 729,486

Int. Cl. Htilh 7/08, 43/02 US. Cl. 335-64 10 Claims ABSTRACT OF THEDISCLOSURE This application is a continuation-in-part of copendingapplication Ser. No. 545,434, filed Apr. 26, 1966 which is in turn acontinuation-in-part of the then copending application Ser. No. 377,993,filed June 25, 1964, now US. Patent 3,251,232.

The present invention is directed to an improved electromagnetic circuitbreaker which will not trip out when subjected to high amplitude currentfor a short time. The circuit breaker incorporates a balanced inertiawheel for effectively increasing the inertia of the circuit breakerarmature to introduce a time delay before the breaker trips out whensubjected to very high overload currents.

As is well known, circuit breakers are used in numerous devices where itis desired to protect electrical equipment against overload. Importantadvantages include the fact that the conventional electromagneticcircuit breaker is resettable and may be tripped repeatedly without anynecessity for replacement or repair. However, one of the disadvantagesof the electromagnetic circuit breakers is that they have a tendency totrip out when subjected to high amplitude current for a short time. Thisis often referred to as nuisance tripping and occurs in some cases inconjunction with the starting of certain types of electrical motors andinductive and capacitive loads.

The present invention provides a device for overcoming this nuisancetripping so that the circuit breaker is substantially insensitive tovery high amplitude currents which last for only a short time. At thesame time, the device of the present invention preserves the otheradvantageous features of the more conventional circuit breaker includingits response to small overloads and to large overloads of long duration.This is accomplished by introducing into the circuit breaker in a simpleand inexpensive manner, an increased mechanical delay which only has asignificant effect for overloads in excess of about 400% of ratedcurrent for the breaker. As the result, the breaker has the capacity totake electrical pulses of higher amplitude and/or longer electricalpulse duration before tripping.

The increase in capacity is achieved through the provision of aninertial wheel in the breaker to introduce an additional time delay.That is, a certain predetermined amount of force is required to move thearmature, operate the mechanism, and open the contacts in a conventionalcircuit breaker. The provision of a balanced inertia wheel in thecircuit breaker increases the dynamic mass of the breaker mechanism butdoes not change the amount 3,497,838 Patented Feb. 24, 1970 ice of forcerequired to operate the breaker. Thus, since the force required tooperate the mechanism is essentially the same with or without theinertia wheel, but the dynamic mass of the mechanism is increased by themass of the inertia wheel, the acceleration is decreased. The result isthat a mechanical time delay is introduced into the circuit breakerwhich, in many cases of high amplitude current, is sufficiently long toprevent the breaker from tripping and allow the short duration highsurge of current to pass. If, however, the surge of current continuesfor some reason, the circuit breaker of the present invention will trip.

When subjected to overload currents at or below about 400% of the ratedcurrent, the circuit breaker of the present invention maintains thespecified calibration of a circuit breaker not having an inertia wheel.This is because the inertia wheel is balanced and does not exert anyappreciable force on the armature. It is only at currents above 400% ofrated current that the inertia wheel begins to have a significant affecton the trip time of the breaker.

It is therefore one object of the present invention to provide a circuitbreaker having improved operating characteristics.

Another object of the present invention is to provide a circuit breakerhaving increased capacity to take electrical pulses of higher amplitudeand/or longer electrical duration, as compared with similar conventionalcircuit breakers.

Another object of the present invention is to provide a circuit breakerhaving an increased time delay for overload currents in excess of about400% of rated current.

Another object of the present invention is to provide a simplified andinexpensive arrangement for incorporating, in a circuit breaker, anadditional mechanical time delay without at the same time significantlymodifying the amount of force required to trip the breaker.

Another object of the present invention is to provide a circuit breakerwith a balanced inertia wheel coupled to the breaker armature, therebyeffectively increasing the dynamic mass of the armature.

These and further objects and advantages of the invention will be moreapparent upon reference to the following specification, claims andappended drawings wherein:

FIGURE 1 is a perspective view of a circuit breaker in its housingconstructed in accordance with the present invention;

FIGURE 2 is a side view of the breaker of FIGURE 1 with the housingremoved, showing the breaker mechanism in relatched open position withthe contacts open;

FIGURE 3 is a partial sectional view similar to that of FIGURE 2,showing the mechanism in a position where the contacts are closed;

FIGURE 4 is a partial sectional view similar to FIG- URES 2 and 3,showing the mechanism in an intermediate or tripped open position;

FIGURE 5 is a vertical cross section taken along line 55 of FIGURE 2;

FIGURE 6 is an enlarged section taken along lines 6-6 of FIGURE 2, butshowing the threaded ferrule in place;

FIGURE 7 is an enlarged perspective view showing the detail of the searpin and striker bar assembly;

FIGURE 8 is a detailed view showing engagement of the sear pin andstriker bar assembly with the forked lever of the breaker of FIGURE 1;

FIGURE 9 is an enlarged perspective view of the electro magnet armaturebell crank assembly;

FIGURE 10 is an enlarged view of the inertia wheel mounted on itssupport; and

FIGURE 11 is an exploded view showing the details of the inertia wheeland axle rivet on which it rotates.

Referring to the drawings, the novel circuit breaker of the presentinvention, illustrated in FIGURE 1, comprises a housing 10, which isformed of a molded plastic having good electrical insulating properties.Supported in the housing is a frame 11 upon which is mounted theoperating elements of the circuit breaker to move a movable contact 12into and out of engagement with a fired contact 13.

Movable contact 12 is secured to a lever 14 pivotally and slidablymounted on the frame by a pin 15 passing through an elongated opening 16in the lever. Pin 15 is mounted on the frame 11, intermediate its endswhile the ends extend beyond the frame and fit snugly into cooperatingrecesses 17, molded in the housing halves 10 and 10 as seen in FIGURE 5.A spring 18 is wound around pin 15 and is provided with a biasing arm 19hearing against the lever 14 and with a reaction arm 20 bearing againstthe frame 11. Portions of the frame 11 are omitted in FIGURES 3 and 4for the sake of clarity. The entire frame 11 is illustrated in FIGURE 2.

An actuating lever 21 is pivotally mounted on the frame 11 by a pin 22.The pin 22 is mounted in the frame intermediate its ends while the endsextend beyond the frame and fit snugly into cooperating recesses 22'molded in the housing 10 as best seen in FIGURE 5. A spring 23 is woundaround the pin 22 and has a biasing arm 24 bearing against a pin 25 andalso a reaction arm 26 bearing against the frame 11. Pivotally mountedon pin 25 is an L-shaped link 27 and this link is pivotally connected toa spaced pair of links 28 by pin 29. The links 28 are pivotallyconnected by a pin 30 to straddle the lever 14.

Rotatably supported in link 27 at the bend of the L is the shaft of asear pin 31 which sear pin is provided with a reduced section 32 betweenthe links which is provided by grinding a fiat sufrace 32 on the shaft31 (FIGURE 7) which acts as a sear for edge 42 of a forked cam lever 40.An arm or striker bar 33 is mounted rigidly and non-rotatably on shaft31 and carries a tab 34 bent up from the end of the arm. One end ofshaft 31 is square to accommodate the square hole in arm 33. Afterassembly, the end of shaft 31 is peened tight against arm 33,permanently keying the shaft and arm together. A spring 35 is woundaround shaft 31 and is provided with arms 36 and 37 bearing respectivelyagainst a stop 38 integral with one arm of link 27 and against anextension 39 of arm 33. The spring is wound to urge extension 39 againstthe stop.

Forked lever 40 is pivotally mounted on pin 25 between the parallel armsof link 27. One leg 41 of the fork is provided with an edge portion 42for engagement with the sear portion 32 of shaft 31, and the other leg43 of the fork is provided with a curved cam section 44 for engagementwith a pin 45 carried by links 28. Between the legs at the end of camsection 44 is a locking recess 46.

Frame 11 is provided with a shelf 47 on which is mounted anelectromagnet 48 having a winding, one end of which is connected inseries with a terminal 49 and the other end in series with a braidedflexible copper wire 50 secured to lever 14, for completing a circuitthrough movable contact 12, fixed contact 13, and contact support 51 toterminal 52. An armature 53 is pivotally mounted on the frame by a pin54 and is secured to an armature lever 55 to form therewith a bell crank'56 shown in detail in FIGURE 9. A spring 57 is mounted on pin 54 tobias the bell crank 56 toward the position shown in FIGURE 2. The freeend of the armature lever forms an arcuate trigger cam surface 58. Inthe closed contact position, the linkage is in the position shown inFIGURE 3 with the tab portion 34 adjacent the arcuate trigger camsurface 58 at the end of armature lever 55.

Referring to FIGURES l0 and 11, the armature bell crank 56 pivots aboutpin 54 secured to frame 11. Slot 84 in the bell crank receives aprojection or pin 83 mounted on a brass inertia wheel 82. Wheel 82 ismounted for rotation on an axle rivet 81 which pases through a centralaperture 86 in the wheel and through a suitable aperture in a flatsupport plate soldered or otherwise rigidly attached to frame 11. Wheel82 is preferably balanced about its rotational axis 87 and is cut awayas at 88 and 89 so that the bell crank 56 acts through the center of thewheel. In this way, the wheel is completely balanced so that it can berotated by the bell crank without exerting any substantial retardingforce on the crank, other than that due to rotary inertia of the wheel.

The housing is formed of two mirror image sections 10 and 10' (FIGURES 1and 5) which are secured together by rivets 62 passing through openingsin the housing. One of the sections, such as section 10, is providedwith an elongated groove 70 and the other section is provided with anelongated tongue which is snugly received in the groove. Thistongue-in-groove arrangement is for the purpose of accurately aligningthe housing sections in assembly.

Each housing section is provided with recesses 63 molded in the meetingfaces. The recesses 63 are provided with an enlarged portion 64. Whenthe sections are secured together as shown in FIGURE 5, the recesses 63combine to provide openings which receive threaded metal ferrules 65(FIGURE 6) with hexagonal heads by which the assembly is secured to asupport. The recesses 66 combined to provide openings for the receptionof the threaded terminals 49 and 52.

In operation, on overload, the electromagnet 48 is energized to a pointwhere it attracts armature 53 and causes the bell crank 56 to rotatecounterclockwise about pin 54. Slot 84 in the leg of the bell crankshown in FIGURE 9, engages with crank pin 83 of the inertia wheel 82.The inertia wheel 82 is attached to the support plate 80 by axle rivet 1but freely rotates about the rivet.

Before the armature 53 can rotate to a point where it will trip thebreaker mechanism, it has to rotate the balanced inertia wheel 82 in aclockwise direction in FIG- URE 10. Under conditions of high currentoverload through the electromagnet 48, the inertia wheel 82 increasesthe length of time it takes to rotate the armature 53 as compared to acircuit breaker not having an inertia wheel. However, under conditionsof low cuirent overload, the inertia wheel 82 does not restrict thetravel of armature 53 via the bell crank and the time required for thearmature 53 to rotate is substantially the same as a similar breaker nothaving an inertia wheel.

When armature 53 rotates counterclockwise, the armature lever 55 (FIGURE9) brings the trigger cam surface 58 into contact with tab 34 to rotatestriker bar 33 and shaft 31. Rotation of shaft 31 presents the reducedsection 32 to the edge 42 of the fork 40, allowing the fork 40 to rotatecounterclockwise about pin 25 to release pin 45 from recess 46 asillustrated in FIGURE 4. The release of pin 45 allows the linkage tocollapse and the lever 14 to pivot about pin 15 to separate the contacts12 and 13. The are drawn by the separating contacts is extinguished byits reaction to the arc chutes 59 and 60 in the usual manner. Ventopening 67 is provided in the casing 10 closely adjacent the arc chutesand serves as a pressure release for the gases produced by arcing. Theforce of spring 23 reacts against pin 25 to rotate the lever 21 to theposition shown in FIGURE 2. The movement of pin 25 about pin 22, underthe urging of spring 23, realigns links 27 and 28 and fork 40 to replacepin 45 in recess 46 as shown in FIGURE 2. In order to close thecontacts, the handle is rotated clockwise about pin 22 to force thelinkage down to rotate lever 14. When the contacts close, they become apivot about which lever 14 is rotated against the force of spring 18 toload the spring and linkage for future toggle action.

It is apparent from the above that the present invention provides animproved circuit breaker, particularly insensitive to short durationhigh overloads. A balanced inertia wheel effectively increases thedynamic inertia of the bell crank 56 and its armature 53 and isparticularly etfective at overloads exceeding 400% of the rated currentto increase the trip time of the circuit breaker. That is, according tothe basic formula F=MA, the increase in mass afiorded by the inertiawheel 82 under the influence of the same tripping force, reduces theacceleration of the armature so that it takes longer to move to aposition where the breaker is tripped. The inertia device of thisinvention is of relatively simple and inexpensive construction andrequires no modification of the basic circuit breaker mechanism. At thesame time, it substantially increases the capacity of the breaker toresist overload currents and substantially reduces the so-callednuisance tripping previously encountered in conventional circuitbreakers.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is, therefore, to be considered in all respects asillustrative and not rectrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is: t

1. In a circuit breaker having an electromagnet and a contact tripmechanism, a bell crank pivoted adjacent said electromagnet including afirst portion forming an armature for said electromagnet, said bellcrank including a second portion for actuating said trip mechanism aftera predetermined amount of movement of said crank, and pivotally mountedbalanced inertia means coupled to said bell crank for efiectivelyincreasing its dynamic mass to overload currents in excess of about 400%of the rated current through said electromagnet.

2. Apparatus according to claim 1 wherein said inertia means comprises abalanced inertia wheel mounted for is rotatably mounted in the pivotalplane of said bell crank.

6. A circuit breaker for protecting against electrical overloadscomprising an electromagnet, a pair of contacts, a toggle mechanismcoupled to one of said contacts for moving said one contact away fromthe other of said contacts, an armature pivoted adjacent saidelectromagnet and including means for tripping said toggle mechanism,and pivotally mounted balanced inertia means coupled to said armaturefor increasing the trip time of said breaker for currents through saidelectromagnet in excess of approximately 400% of its rate current.

7. A breaker according to claim 6 wherein said inertia means comprises abalanced inertia wheel mounted for rotation about a fixed axis adjacentsaid armature.

8. A circuit breaker comprising an electrically insulating housing, anelectromagnet mounted in said housing,

a pair of contacts in said housing, a toggle mechanism in said housingfor moving one of said contacts away from the other, said togglemechanism including a sear, a bell crank pivoted adjacent saidelectromagnet for tripping said sear, a portion of said bell crankforming an armature for said electromagnet, a balanced inertia wheelmounted for rotation about a fixed axis in said housing, and meanscoupling said bell crank to said inertia wheel whereby pivotal movementof said bell crank causes said inertia wheel to rotate.

9. A circuit breaker according to claim 8 wherein said wheel carries aprojection, said bell crank having a slot slidably received in saidprojection.

10. A circuit breaker according to claim 8 wherein said wheel isrotatably mounted in the pivotal plane of said bell crank.

References Cited UNITED STATES PATENTS 1,554,652 9/1925 Pons 200-331,774,966 9/1930 Eaton 335-64 2,064,657 12/1936 Goff 335-64 898,649 9/1908 Higughi 58-28 FOREIGN PATENTS 259,580 6/ 1949 Switzerland.

BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner

